Electrolysis cell for generating halogen (and particularly chlorine) dioxide in an appliance

ABSTRACT

A method for making chlorine dioxide, by passing an aqueous feed solution comprising sodium chlorite into a non-membrane electrolysis cell comprising an anode and a cathode, adjacent to the anode, while flowing electrical current between the anode and the cathode to electrolyze the aqueous feed solution and convert the halogen dioxide salt to halogen dioxide. The anode is preferably a porous anode through which the aqueous feed solution passes to maximize the conversion of chlorite to chlorine dioxide.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation in part of U.S. applicationSer. No. 09/947,846, filed on 06 Sep. 2001.

FIELD OF THE INVENTION

[0002] This invention relates to devices for generating halogen dioxide,preferably chlorine dioxide, from aqueous solutions containing a halogendioxide salt, preferably chlorite salts, suitable for interface with anappliance, and particularly a refrigerator.

BACKGROUND OF THE INVENTION

[0003] Chlorine dioxide, ClO₂, is one of the most effective bleachingagents for use in industrial and domestic process and services, and forcommercial and consumer products. The strong oxidative potential of themolecule makes it ideal for a wide variety of uses that includedisinfecting, sterilizing, and bleaching. Concentrations of chlorinedioxide in an aqueous solution as low as 1 part per million (ppm) orless, are known to kill a wide variety of microorganisms, includingbacteria, viruses, molds, fungi, and spores. Higher concentrations ofchlorine dioxide, up to several hundred ppms, provide even higherdisinfection, bleaching and oxidation of numerous compounds for avariety of applications, including the paper and pulp industry, wastewater treatment, industrial water treatment (e.g. cooling water),fruit-vegetable disinfection, oil industry treatment of sulfites,textile industry, and medical waste treatment.

[0004] Chlorine dioxide offers advantages over other commonly usedbleaching materials, such as hypochlorite and chlorine. Chlorine dioxidecan react with and break down phenolic compounds, and thereby removingphenolic-based tastes and odors from water. Chlorine dioxide is alsoused in treating drinking water and wastewater to eliminate cyanides,sulfides, aldehydes and mercaptans. The oxidation capacity of ClO2, interms of available chlorine, is 2.5 times that of chlorine. Also, unlikechlorine/hypochlorite, the bactericidal efficiency of chlorine dioxideremains generally effective at pH levels of 6 to 10. Additionally,chlorine dioxide can inactivate C. parvum oocysts in water whilechlorine/hypochlorite cannot. Hypochlorite and chlorine both react withthe bleached target by inserting the chlorine molecule into thestructure of the target. Though this mode of reaction can be effective,it can result in the formation of one or more chlorinated products, orby-products, which can be undesirable both from a economic sense (toeliminate hydrocarbons from the reaction media) and a safety andenvironmental standpoint. In addition, the step of bleaching byhypochlorite and chlorine results in the destruction of the bleachspecies itself, such that subsequent bleaching requires a fresh supplyof the chlorine bleach. Another disadvantage is that certainmicroorganisms that are intended to be killed by these two commonly-usedbleach materials can develop a resistance over time, specifically atlower concentrations of the chlorine or hypochlorite.

[0005] Chloride dioxide is generally used in an aqueous solution atlevels up to about 35%. It is a troublesome material to transport andhandle at high aqueous concentrations, due to its low stability and highcorrosivity. This has required end users to generate chlorine dioxide ondemand, usually employing a precursor such as sodium chlorite (NaClO₂)or sodium chlorate (NaClO₃).

[0006] A typical process for generating chlorine dioxide from sodiumchlorate salt is the acid-catalyzed reaction:

NaClO₃+2HCl→NaCl+½Cl₂+ClO₂+H₂O

[0007] Sodium chlorite is easier to convert to chlorine dioxide. Atypical process for generating chlorine dioxide from sodium chloritesalt is the acid-catalyzed reaction:

5NaClO₂+4HCl→4ClO₂+5NaCl+2H₂O

[0008] Further details on the acid-catalyzed reactions of chlorites andchlorates to produce chlorine dioxide can be found in “Chlorine DioxideGeneration Chemistry” (A. R. Pitochelli, Rio Linda Chemical Company),Third International Symposium: Chlorine Dioxide Drinking Water, ProcessWater and Wastewater Issues, September 14, 15, 1995, La Meridian Hotel,New Orleans, La., incorporated herein by reference.

[0009] A common method of making chlorine dioxide uses a multi-chamberelectrolysis cell that converts the chlorite salt into chlorine dioxide.This method uses separately an anode compartment and a cathodecompartment that are separated by an ion permeable membrane. Theseparate compartments operate with significantly different reactants,and contain solutions with different pH values. One example of amulti-compartment electrolysis cell is disclosed in U.S. Pat. No.4,456,510, issued to Murakami et al. on Jun. 26, 1984, which teaches aprocess for forming chlorine dioxide by electrolyzing a solution ofsodium chlorite in an electrolysis cell that contains an anodecompartment and a cathode compartment separated by a diaphragm,preferably a cation exchange membrane. Another example of a two-chamberelectrolysis cell is disclosed in U.S. Pat. No. 5,158,658, issued toCawlfield, et al. on Oct. 27, 1992 which describes a continuouselectrochemical process and an electrolytic cell having an anode chamberhaving a porous flow-through anode, a cathode chamber, and a membranethere between.

[0010] While separate-compartment, membrane-containing electrolysiscells have been used to make chlorine dioxide on a commercial scale,they have not been completely satisfactory. Even though they may haveconvenience advantages over the conventional acid catalysis productionof chlorine dioxide, the electrochemical approach has proven to be moreexpensive to produce large volumes of chlorine dioxide. The electrolysiscells in commercial use, and disclosed in the prior art that utilize ionpermeable membranes or diaphragms, require that the anolyte solution besubstantially free of divalent cations, such as magnesium and calcium,to avoid the formation of precipitated calcium or magnesium salts thatwould quickly block and cover the membrane, and significantly reduce orstop the electrolysis reaction.

[0011] There remains a need for a simple, safe method and apparatus formanufacturing chlorine dioxide to meet a wide variety of commercial anddomestic uses, under a wide variety of situations. This need wassubstantially met via the filing of U.S. patent application Ser. No.09/947,846, filed on 06 Sep. 2001, directed to an Electrolysis Cell forGenerating Chlorine Dioxide. Nevertheless, there remains a significantneed to identify electrolysis devices and/or cells suitable forinterface with common household appliances. Such electrolysis devicesand/or cells can be used to disinfect water that is employed and/ordispensed by an appliance, thereby reducing the need for upstream and/ordownstream water purification and/or sanitization devices.

SUMMARY OF THE INVENTION

[0012] The present invention relates to apparatuses for making halogendioxide from an aqueous solution comprising a halogen dioxide salt,using a non-membrane electrolysis cell, in an appliance. A non-membraneelectrolysis cell is an electrolysis cell that comprises an anodeelectrode and a cathode electrode, and having a cell chamber, and whichdoes not have an ion permeable membrane that divides the cell passageinto two (or more) distinct anode and cathode chambers. The halogendioxide salt is converted to the halogen dioxide as electricity passesthrough the aqueous feed solution in a passage that forms a portion ofthe cell chamber adjacent to the surface of the anode.

[0013] In present invention further relates to electrolysis apparatusesand/or cells suitable for interface with an appliance. The interface ofthe electrolytic apparatuses and/or cells disclosed herein with anappliance serves to disinfect and/or sterilize one or more parts of saidappliance, the contents of said appliance, and/or water delivered toand/or from said appliance. For purposes of the present disclosure, anappliance is defined as a device designed for home use, comprising asource of electrical or other power necessary for executing the definedfunctions of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The various advantages of the present invention will becomeapparent to skilled artisans after studying the following specificationand by reference to the drawings in which:

[0015]FIG. 1 shows an electrolysis cell used in the practice of thepresent invention.

[0016]FIG. 2 shows a sectional view of the electrolysis cell of FIG. 1though line 2-2.

[0017]FIG. 3 shows a sectional view of an alternative electrolysis cellused in the practice of the present invention.

[0018]FIG. 4 is a sectional view of another electrolysis cell having aporous anode.

[0019]FIG. 5 is a sectional view of yet another electrolysis cell havinga porous anode.

[0020]FIG. 6 is a sectional view of another electrolysis cell having aporous anode and a porous flow barrier.

[0021]FIG. 7 is a sectional view of yet another electrolysis cell havinga porous anode and a porous flow barrier.

[0022]FIG. 8 is a sectional view of still another electrolysis cellhaving a porous anode and a porous flow barrier.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention employs an electrical current passingthrough an aqueous feed solution between an anode and a cathode toconvert the halogen dioxide salt precursor dissolved within the solutioninto a halogen dioxide. When an aqueous solution flows through thechamber of the electrolysis cell, and electrical current is passedbetween the anode and the cathode, several chemical reactions occur thatinvolve the water, as well as one or more of the other salts or ionscontained in the aqueous solution.

[0024] At the anode, within a narrow layer of the aqueous solution inthe passage adjacent to the anode surface, the following reactionoccurs:

6H₂O

O₂(g)+4H₃O⁺+4e⁻.

[0025] Without being bound by any particular theory, it is believed thatthe anode electrode withdraws electrons from the water adjacent to theanode, which results in the formation of H₃O⁺ species in the narrowsurface layer of aqueous feed solution. The H₃O⁺ species react with thechlorine dioxide salt, for example, sodium chlorite, to generatechlorine dioxide in the aqueous solution within the passage at the anodesurface region. This surface layer is believed to be about 100nanometers in thickness. Flow dynamics, which include the movement ofmolecules in a flowing solution by turbulence, predict that theconversion of chlorite salts to chlorine dioxide will increase as thesolution flow path nears the anode surface layer. Consequently,electrolysis cells and electrolysis systems of the present inventionpreferably maximize the flow of the aqueous feed solution through thissurface layer adjacent the anode, in order to maximize the conversion ofchlorite to chlorine dioxide.

[0026] Although the present invention relates to halogen dioxide productand can include iodine dioxide, bromine dioxide and fluorine dioxide,the more common and most preferred product is chlorine dioxide.

[0027] The precursor material from which the halogen dioxide is formedis referred to as a halogen dioxide salt. The more common and mostpreferred halogen dioxide salt is the corresponding halite salt of thegeneral formula MXO₂, wherein M is selected from alkali and alkali-metalearth metal, and is more commonly selected from sodium, potassium,magnesium and calcium, and is most preferably sodium; and wherein X ishalogen and is selected from Cl, Br, I and F, and is preferably Cl. Thehalogen dioxide salt can comprise two or more salts in various mixtures.

[0028] The aqueous feed solution comprises the halogen dioxide salt,which for simplicity will be exemplified herein after by the mostpreferred halite salt, sodium chlorite. Sodium chlorite is not a saltordinarily found in tap water, well water, and other water sources.Consequently, an amount of the sodium chlorite salt is added into theaqueous feed solution at a desired concentration generally of at least0.1 ppm.

[0029] The level of chlorite salt comprised in the aqueous feed solutioncan be selected based on the required bleaching or disinfection requiredby the chlorine dioxide, in addition to the conversion efficiency of theelectrolysis cell to convert the sodium chlorite to the product chloridedioxide. The level of sodium chlorite is generally from about 1 ppm toabout 10,000 ppm. For disinfection of a water source, a sodium chloritelevel is preferably from about 1 ppm to about 5000 ppm, and morepreferably about 10 ppm to about 1000 ppm. The resulting halogen dioxideproduct level is from about 0.1 ppm to about 10,000 ppm, preferably fromabout 1 ppm to about 200 ppm. For bleaching purposes, a sodium chloritelevel of from about 100 ppm to about 10,000 ppm is preferred.

[0030] The range of chlorine dioxide conversion that is achievable inthe electrolysis cells of the present invention generally ranges fromless than about 1% to about 99%. The level of conversion is dependentmost significantly on the design of the electrolysis cell, herein afterdescribed, as well as on the electrical current properties used in theelectrolysis cell.

[0031] The aqueous feed solution can comprise de-ionized water, andsubstantially no chloride (Cl⁻) or other halide ions, which uponelectrolysis can form chlorine or a mixed oxidant, includinghypochlorite. Preferably, aqueous effluent comprises less than about 1.0ppm, and more preferably less than 0.1 ppm, of chlorine.

[0032] The aqueous feed solution can optionally comprise one or moreother salts in addition to the sodium chlorite. These optional salts canbe used to enhance the disinfection and bleaching performance of theeffluent that is discharged from the electrolysis cell, or to provideother mixed oxidants in response to the passing of electrical currentthrough the electrolysis cell. A preferred other salt is an alkalihalide, that is most preferably a sodium chloride. A preferred apparatusand method for electrolyzing aqueous solutions comprising alkali halidesis disclosed in co-pending, commonly-assigned U.S. provisional patentapplication 60/280,913 (Docket 8492P), filed on Apr. 2, 2001.

[0033] The aqueous feed solution comprising the sodium chlorite can beprovided in a variety of ways. A solid, preferably powdered, form of thesodium chlorite can be mixed into an aqueous solution to form adissolved solution, which can be used as-is as the aqueous feed solutionor, if in a concentrated solution can be subsequently diluted withwater. Preferably, a concentrated solution of about 2% to about 35%sodium chlorite can be used.

[0034] The present invention can optionally use a local source ofhalogen dioxide salt, and a means for delivering the halogen dioxidesalt to the aqueous feed solution. This embodiment is advantageouslyused in those situations when the target water to be treated with theelectrolysis cell does not contain a sufficient amount, or any, of thehalogen dioxide salt. The local source of halogen dioxide salt can bereleased into a stream of the aqueous solution, which then passesthrough the electrolysis cell. The local source of halogen dioxide saltcan also be released into a portion of a reservoir of aqueous solution,which portion is then drawn into the electrolysis cell. Preferably, allthe local source of halogen dioxide salt passes through the electrolysiscell, to maximize the conversion to halogen dioxide, and to limit theaddition of salts to the reservoir generally. The local source ofhalogen dioxide salt can also supplement any residual levels of halogendioxide salt already contained in the aqueous solution.

[0035] The local source of halogen dioxide salt can be a concentratedbrine solution, a salt tablet in fluid contact with the reservoir ofelectrolytic solution, or both. A preferred local source of halogendioxide salt is a solid or powdered material. The means for deliveringthe local source of halogen dioxide salt can comprise a salt chambercomprising the halogen dioxide salt, preferably a pill or tablet,through which a portion of the aqueous solution passes, therebydissolving a portion of the halogen dioxide salt to form the aqueousfeed solution. The salt chamber can comprise a salt void formed in thebody of the device that holds the electrolysis cell, which is positionedin fluid communication with the portion of aqueous solution that willpass through the electrolysis cell.

[0036] In certain circumstances, a preferred halogen dioxide salt has areduced solubility in water, compared to sodium chlorite, to control therate of dissolution of the halogen dioxide salt. Examples of preferredhalogen dioxide salts are the less soluble calcium chlorite andmagnesium chlorite salts. A pill or tablet can also be formulated withother organic and inorganic materials to control the rate of dissolutionof the halogen dioxide salt. Preferred is a slow dissolving salt tablet,to release sufficient halogen dioxide salt to form an effective amountof halogen dioxide product. The release amount of the halogen dioxidesalt is typically, between 1 milligram to 10 grams halogen dioxide salt,for each liter of solution passed through the electrolysis cell. Thehalide pill can be a simple admixture of the halogen dioxide salt withthe dissolution control materials, which can be selected from variouswell-known encapsulating materials, including but not limited to fattyalcohol, fatty acids, and waxes.

[0037] Any water source can be used to form the aqueous feed solution,including well water, tap water, softened water, and industrial processwater, and waste waters. However, for many applications of theinvention, distilled or de-ionized water is most preferred to form aneffluent solution with essentially only chlorine dioxide active. Sincedistilled and de-ionized water do not contain any of a variety of othersalts, including sodium chloride, appreciable amounts of other mixedoxidants will not be formed. Even in those situations where one prefersto include other salts, including sodium chloride, in solution with thesodium chlorite, de-ionized water is more preferred, as it allows forbetter control of the types and amounts of the salts being passedthrough the electrolysis cell.

[0038] The addition of other salts or electrolytes into the selectedwater source will increase the conductivity of the water, which willincrease the amount of chlorine dioxide, and any mixed oxidants,produced. However, the increase in conductivity may not result in ahigher productivity efficiency, since the increase in conductivity willincrease the current draw. Therefore, while more chlorine dioxide willbe produced, more power will be drawn. A suitable chlorine dioxideproductivity equation is expressed by equation I,

η=(CClO₂ Q)/(I*V)  (I)

[0039] wherein:

[0040] η units are micrograms of chlorine dioxide per minute, per wattof power used;

[0041] CClO₂ is the concentration of the generated chlorine dioxide inmilligrams per liter (mg/l);

[0042] I is the electric current in amps;

[0043] Q is the volumetric flow rate in milliliters per minute (ml/m);and

[0044] V is electric potential across the cell in volts.

[0045] The pH of the aqueous feed solution containing the halogendioxide salt is preferably above about 3, and more preferably aboveabout 5. If the pH of the aqueous feed solution is too low, the sodiumchlorite, for example, can begin to react with the hydronium ions in thefeed solution and convert to chlorine dioxide, even before entering theelectrolysis cell. The aqueous feed solution is preferably maintained ata pH of less than 10, and more preferably at a pH of less than 8. Mostpreferably, the pH of the feed solution is between about 6 and 8.

[0046] The present invention is particularly well suited for thepreparation of aqueous effluents containing chlorine dioxide when theaqueous feed solution is a water source that contains calcium and otherdivalent salts that can precipitate salts as a by-product of the waterelectrolysis. Because the present electrolysis cell does not have an ionpermeable membrane separating the cell into separate anode and cathodechambers, there is reduced risk that the precipitation of calcium orother divalent salt will inhibit or stop the electrical current flow andthe conversion of halite to halogen dioxide.

[0047] The aqueous feed solution containing the sodium chlorite can befed to the electrolysis cell from a batch storage container.Alternatively, the feed solution can be prepared continuously byadmixing a concentrated aqueous solution of sodium chlorite with asecond water source, and passing continuously the admixture to theelectrolysis cell. Optionally, a portion of the aqueous feed solutioncan comprise a recycled portion of the effluent from the electrolysiscell. And, the aqueous feed solution can comprise a combination of anyof the forgoing sources. The aqueous feed solution can flow continuouslyor periodically through the electrolysis cell.

[0048] Electrolysis Cell

[0049] The electrolysis cell generates chlorine dioxide from the sodiumchlorite by flowing electrical current through the aqueous feed solutionthat passes through the cell chamber. The electrolysis cell comprises atleast a pair of electrodes, an anode and a cathode. The cell alsocomprises a cell chamber through which the aqueous feed solution passes,and includes a passage that is adjacent to the anode. The passageincludes the narrow surface layer adjacent to the anode surface wherethe conversion reaction occurs. It is preferred to pass as much of themass of the aqueous effluent solution through the passage and its narrowanode surface region as possible.

[0050] In one embodiment of the present invention, the cell comprises ananode and a confronting (and preferably, co-extensive) cathode that areseparated by a cell chamber that has a shape defined by the confrontingsurfaces of the pair of electrodes. The cell chamber has a cell gap,which is the perpendicular distance between the two confrontingelectrodes. Typically, the cell gap will be substantially constantacross the confronting surfaces of the electrodes. The cell gap ispreferably 0.5 mm or less, more preferably 0.2 mm or less.

[0051] The electrolysis cell can also comprise two or more anodes, ortwo or more cathodes. The anode and cathode plates are alternated sothat an anode is confronted by a cathode on each face, with a cellchamber there between. Examples of electrolysis cells that can comprisea plurality of anodes and cathodes are disclosed in U.S. Pat. No.5,534,120, issued to Ando et al. on Jul. 9, 1996, and U.S. Pat. No.4,062,754, issued to Eibl on Dec. 13, 1977, which are incorporatedherein by reference.

[0052] Generally, the electrolysis cell will have one or more inletopenings in fluid communication with each cell chamber, and one or moreoutlet openings in fluid communication with the chambers. The inletopening is also in fluid communication with the source of aqueous feedsolution, such that the aqueous feed solution can flow into the inlet,through the chamber, and from the outlet of the electrolysis cell. Theeffluent solution (the electrolyzed aqueous feed solution that exitsfrom the electrolysis cell) comprises an amount of chlorine dioxide thatwas converted within the cell passage in response to the flow ofelectrical current through the solution. The effluent solution can beused as a source of chlorine dioxide, for example, for disinfecting orbleaching articles, or for treating other volumes of water or aqueoussolutions. The effluent can itself be a treated solution, where the feedsolution contains microorganisms or some other oxidizable sourcematerial that can be oxidized in situ by the chlorine dioxide that isformed.

[0053] The present invention also provides a halogen dioxide generatingsystem, comprising:

[0054] a) a source of an aqueous feed solution comprising a halogendioxide salt;

[0055] b) a non-membrane electrolysis cell having a cell chamber, andcomprising an anode and a cathode, the cell chamber having a passageadjacent to the anode, and an inlet and an outlet in fluid communicationwith the cell chamber;

[0056] c) a means for passing the aqueous feed solution into the cellchamber, along the passage, and out of the outlet; and

[0057] d) an electric current supply to flow a current through theaqueous solution in the chamber, to convert a portion of the halogendioxide salt in the passage to halogen dioxide, and thereby form anaqueous effluent comprising halogen dioxide.

[0058]FIG. 1 and FIG. 2 show an embodiment of an electrolysis cell 10 ofthe present invention. The cell comprises an anode 21 electrode, and acathode 22 electrode. The electrodes are held a fixed distance away fromone another by a pair of opposed non-conductive electrode holders 30having electrode spacers 31 that space apart the confrontinglongitudinal edges of the anode and cathode to form a cell chamber 23having a chamber gap. The chamber 23 has a cell inlet 25 through whichthe aqueous feed solution can pass into of the cell, and an opposed celloutlet 26 from which the effluent can pass out of the electrolysis cell.The assembly of the anode and cathode, and the opposed plate holders areheld tightly together between a non-conductive anode cover 33 (shownpartially cut away) and cathode cover 34, by a retaining means (notshown) that can comprise non-conductive, water-proof adhesive, bolts, orother means, thereby restricting exposure of the two electrodes only tothe electrolysis solution that flows through the chamber 23. Anode lead27 and cathode lead 28 extend laterally and sealably through channelsmade in the electrode holders 30.

[0059]FIG. 2 shows cell chamber 23 and the passage 24 along the anode 21surface. The passage 24 is a portion of the cell chamber 23, though itis shown with a boundary 29 only to illustrate its adjacent to the anode21, and not to show the relative proportion or scale relative to thecell chamber.

[0060] Another embodiment of the electrolysis cell of the presentinvention is shown in FIG. 3. This electrolysis cell has an anode outlet35. The anode outlet removes a portion of the electrolyzed feed solutionflowing in the passage 24 adjacent the anode 21 as an anode effluent.The remainder of the cell effluent exits from the cell outlet 26, whichhereafter will also be referred to as the cathode effluent and thecathode outlet, respectively. Similar electrolysis cells that remove aportion of the electrolyzed solution flowing adjacent the anode throughan anode outlet are described in U.S. Pat. No. 5,316,740, issued toBaker et al. on May 31, 1994, U.S. Pat. No. 5,534,120 issued to Ando etal. on Jul. 9, 1996, and U.S. Pat. No. 5,858,201, issued to Otsuka etal. on Jan. 12, 1999. Particularly preferred is an electrolysis cell asshown in FIG. 3 of U.S. Pat. No. 4,761,208 that uses a physical barrier(element 16) positioned between the anode and the cathode adjacent theoutlet, whereby mixing of the solution adjacent the anode with thesolution adjacent the cathode can be minimized or eliminated prior toremoval through the anode outlet. Preferably, the cathode effluent,which will comprise a low level or no chlorine dioxide product, ispassed back to and mixed into the aqueous feed solution.

[0061] An electrode can generally have any shape that can effectivelyconduct electricity through the aqueous feed solution between itself andanother electrode, and can include, but is not limited to, a planarelectrode, an annular electrode, a spring-type electrode, and a porouselectrode. The anode and cathode electrodes can be shaped and positionedto provide a substantially uniform gap between a cathode and an anodeelectrode pair, as shown in FIG. 2. On the other hand, the anode and thecathode can have different shapes, different dimensions, and can bepositioned apart from one another non-uniformly. The importantrelationship between the anode and the cathode is for a sufficient flowof current through the anode at an appropriate voltage to promote theconversion of the halite salt to halogen dioxide within the cell passageadjacent the anode.

[0062] Planar electrodes, such as shown in FIG. 2, have a length alongthe flow path of the solution, and a width oriented transverse to theflow path. The aspect ratio of planar electrodes, defined by the ratioof the length to the width, is generally between 0.2 and 10, morepreferably between 0.1 and 6, and most preferably between 2 and 4.

[0063] The electrodes, both the anode and the cathode, are commonlymetallic, conductive materials, though non-metallic conductingmaterials, such as carbon, can also be used. The materials of the anodeand the cathode can be the same, but can advantageously be different. Tominimize corrosion, chemical resistant metals are preferably used.Examples of suitable electrodes are disclosed in U.S. Pat. No. 3,632,498and U.S. Pat. No. 3,771,385. Preferred anode metals are stainless steel,platinum, palladium, iridium, ruthenium, as well as iron, nickel andchromium, and alloys and metal oxides thereof. More preferred areelectrodes made of a valve metal such as titanium, tantalum, aluminum,zirconium, tungsten or alloys thereof, which are coated or layered witha Group VIII metal that is preferably selected from platinum, iridium,and ruthenium, and oxides and alloys thereof. One preferred anode ismade of titanium core and coated with, or layered with, ruthenium,ruthenium oxide, iridium, iridium oxide, and mixtures thereof, having athickness of at least 0.1 micron, preferably at least 0.3 micron.

[0064] For many applications, a metal foil having a thickness of about0.03 mm to about 0.3 mm can be used. Foil electrodes should be madestable in the cell so that they do not warp or flex in response to theflow of liquids through the passage that can interfere with properelectrolysis operation. The use of foil electrodes is particularlyadvantageous when the cost of the device must be minimized, or when thelifespan of the electrolysis device is expected or intended to be short,generally about one year or less. Foil electrodes can be made of any ofthe metals described above, and are preferably attached as a laminate toa less expensive electrically-conductive base metal, such as tantalum,stainless steel, and others.

[0065] A particularly preferred anode electrode of the presentinventions is a porous, or flow-through anode. The porous anode has alarge surface area and large pore volume sufficient to pass therethrough a large volume of aqueous feed solution. The plurality of poresand flow channels in the porous anode provide a greatly increasedsurface area providing a plurality of passages, through which theaqueous feed solution can pass. Porous media useful in the presentinvention are commercially available from Astro Met Inc. in Cincinnati,Ohio, Porvair Inc. in Henderson, N.C., or Mott Metallurgical inFarmington, Conn. Alternately U.S. Pat. Nos. 5,447,774 and 5,937,641give suitable examples of porous media processing. Preferably, theporous anode has a ratio of surface area (in square centimeters) tototal volume (in cubic centimeters) of more than about 5 cm⁻¹, morepreferably of more than about 10 cm⁻¹, even more preferably more thanabout 50 cm⁻¹ and most preferably of more than about 200 cm⁻¹.Preferably the porous anode has a porosity of at least about 10%, morepreferably of about 30% to about 98%, and most preferably of about 40%to about 70%. Preferably, the porous anode has a combination of highsurface area and electrical conductivity across the entire volume of theanode, to optimize the solution flow rate through the anode, and theconversion of chlorite salt contained in the solution to the chlorinedioxide product.

[0066] The flow path of the aqueous feed solution through the porousanode should be sufficient, in terms of the exposure time of thesolution to the surface of the anode, to convert the chlorite salt tothe chlorine dioxide. The flow path can be selected to pass the feedsolution in parallel with the flow of electricity through the anode (ineither the same direction or in the opposite direction to the flow ofelectricity), or in a cross direction with the flow of electricity. Theporous anode permits a larger portion of the aqueous feed solution topass through the passages adjacent to the anode surface, therebyincreasing the proportion of the halogen dioxide salt that can beconverted to the halogen dioxide product.

[0067]FIG. 4 shows an electrolysis cell comprising a porous anode 21.The porous anode has a multiplicity of capillary-like flow passages 24through which the aqueous feed solution can pass adjacent to the anodesurfaces within the porous electrode. In the electrolysis cell of FIG.4, the aqueous feed solution flows in a parallel direction to the flowof electricity between the anode and the cathode.

[0068] Another embodiment of an electrolysis cell having a porous anodeis shown in FIG. 5. In this embodiment, the flow of aqueous feedsolution is in a cross direction to the flow of electricity between theanode and the cathode. Because the flow passages through the porousanode are generally small (less than 0.2 mm), the flow of a unit ofsolution through a porous anode will require substantially more pressurethat the same quantity flowing through an open cell chamber.Consequently, if aqueous feed solution is introduced into anelectrolysis cell having a porous anode and an open chamber, generallythe amount of solution flowing through the porous anode and across itssurfaces will be significantly diminished, since the solution will flowpreferentially through the open cell chamber.

[0069] To address the above problem where the aqueous feed solution canby-pass the porous anode, the cell chamber is preferably provided, asshown in FIG. 6, with a non-conducting, porous flow barrier 40, withinthe volume of the cell chamber 24 between the cathode 22 and the porousanode 21. The porous barrier 40 is non-conducting, to preventelectricity from short-circuiting between the anode and the cathode viathe chamber material. The porous barrier exerts a solution pressure dropas the aqueous feed solution flows through the cell chamber. The porousbarrier should not absorb or retain water, and should not react with theaqueous solution and chemical ingredients therein, including the halogendioxide products. The porous barrier 40 can be made of a non-conductingmaterial selected from, but not limited to, plastics such aspolyethylene, polypropylene, and polyolefin, glass or other siliceousmaterial, and silicon. The porous barrier can comprise a plurality ofspheres, ovals, and other shaped objects of the same size or ofdifferent sizes, that can be packed loosely, or as a unified matrix ofarticles, into the chamber. FIG. 6 shows the porous barrier 40 as amatrix of spherical objects of varying diameters. The porous barrier 40can also be a one or more baffles, which substantially restrict the flowof the solution through the cell chamber 24. As shown in FIG. 7, suchbaffles can comprise a series of vertical barriers having aperturestherein for restricting the flow of solution. The restricted flow ofaqueous feed solution through the non-conducting, porous barriersignificantly reduces the proportion of aqueous feed solution that canpass through cell chamber, thereby increasing the proportion of halogendioxide salt that is converted in the passages 23 within the porousanode 21.

[0070] While the solution flowing through the porous anode and the cellchamber 24 containing the porous barrier 40 can mix and flow back andforth somewhat between each other, the effluents exiting from thedifferent areas of the outlet end 26 of the cell have substantiallydifferent solution compositions. The effluent 38 exiting the porousanode will have a significantly lower pH and higher conversion ofhalogen dioxide product than the effluent 39 exiting the cell chamberadjacent to the cathode. The effluent 38 exiting the porous anode can beseparated from the effluent 39 and removed from the cell by placing abarrier 37 as shown in FIG. 8.

[0071] Another embodiment of the present invention uses an electrolysiscell that has an open chamber. The open-chamber electrolysis cell isparticularly useful in the practice of the invention in reservoirs ofaqueous feed solution, including pools, bath tubs, spas, tanks, andother open bodies of water. The aqueous feed solution can flow into thecell and to the anode from various directions. The halogen dioxide saltin the aqueous feed solution can be contained in the reservoir solution,or can be delivered into the reservoir solution locally as a localsource of halogen dioxide salt, as herein before described. Examples ofopen-chamber electrolysis cells include those described in U.S. Pat. No.4,337,136 (Dahlgren), U.S. Pat. No. 5,013,417 (Judd), U.S. Pat. No.5,059,296 (Sherman), and U.S. Pat. No. 5,085,753 (Sherman).

[0072] An alternative system for generating halogen dioxide comprises abatch container containing the aqueous feed solution. A re-circulatingpump circulates the feed solution from the container through anelectrolysis cell, and discharges the effluent back to the batchcontainer. In time, the concentration of the un-reacted chlorite salt inthe solution will be reduced to essentially zero, whereby the chargedamount of sodium chlorite in the aqueous feed solution will have beennearly completely converted to chlorine dioxide product. In a slightlydifferent system, the electrolysis cell can be positioned within thebatch container, submerged within the aqueous solution comprising thesodium chlorite. A pump or mixer within the container forces thesolution through the electrolysis cell, and re-circulates the solutionuntil the target conversion of sodium chlorite to chlorine dioxide isachieved.

[0073] The electrolysis cell can also comprise a batch-type cell thatelectrolyses a volume of the aqueous feed solution. The batch-type cellcomprises a batch chamber having a pair of electrodes. The batch chamberis filled with aqueous feed solution comprising the sodium chloritesalt, which is then electrolyzed to form a batch of effluent solutioncontaining chlorine dioxide. The electrodes preferably comprise an outerannular anode and a concentric inner cathode. An example of a suitablebatch cell, for use with a sodium chlorite salt supply in accordancewith the present invention, is disclosed in WO 00/71783-A1, publishedNov. 30, 2000, incorporated herein by reference.

[0074] Electrical Current Supply

[0075] An electrical current supply provides a flow of electricalcurrent between the electrodes and across the passage of aqueous feedsolution passing across the anode. For many applications, the preferredelectrical current supply is a rectifier of household (or industrial)current that converts common 100-230 volt AC current to DC current.

[0076] For applications involving portable or small, personal usesystems, a preferred electrical current supply is a battery or set ofbatteries, preferably selected from an alkaline, lithium, silver oxide,manganese oxide, or carbon zinc battery. The batteries can have anominal voltage potential of 1.5 volts, 3 volts, 4.5 volts, 6 volts, orany other voltage that meets the power requirements of the electrolysisdevice. Most preferred are common-type batteries such as “AA” size,“AAA” size, “C” size, and “D” size batteries having a voltage potentialof 1.5 V. Two or more batteries can be wired in series (to add theirvoltage potentials) or in parallel (to add their current capacities), orboth (to increase both the potential and the current). Re-chargeablebatteries and mechanical wound-spring devices can also be advantageouslyemployed.

[0077] Another alternative is a solar cell that can convert (and store)solar power into electrical power. Solar-powered photovoltaic panels canbe used advantageously when the power requirements of the electrolysiscell draws currents below 2000 milliamps across voltage potentialsbetween 1.5 and 9 volts.

[0078] In one embodiment, the electrolysis cell can comprise a singlepair of electrodes having the anode connected to the positive lead andthe cathode connected to the negative lead of the battery or batteries.A series of two or more electrodes, or two or more cells (each a pair ofelectrodes) can be wired to the electrical current source. Arranging thecells in parallel, by connecting each cell anode to the positiveterminal(s) and each cell cathode to the negative terminal(s), providesthe same electrical potential (voltage) across each cell, and divides(evenly or unevenly) the total current between the two or more electrodepairs. Arranging two cells (for example) in series, by connecting thefirst cell anode to the positive terminal, the first cell cathode to thesecond cell anode, and the second cell cathode to the negative terminal,provides the same electrical current across each cell, and divides thetotal voltage potential (evenly or unevenly) between the two cells.

[0079] The electrical current supply can further comprise a circuit forperiodically reversing the output polarity of the battery or batteriesin order to maintain a high level of electrical efficacy over time. Thepolarity reversal minimizes or prevents the deposit of scale and theplating of any charged chemical species onto the electrode surfaces.Polarity reversal functions particularly well when using confrontinganode and cathode electrodes.

[0080] Chlorine Dioxide Effluent

[0081] The discharged effluent containing the converted chlorine dioxideis removed from the electrolysis cell and is used, for example, as anaqueous disinfection or an aqueous bleaching solution. The effluent canbe used as-made by direct delivery to an oxidizable source that isoxidized by the chlorine dioxide. The oxidizable source can be a secondsource of water or other aqueous solution comprising microorganisms aredestroyed when mixed or contacted with the effluent solution.Microorganisms contained within the aqueous feed solution would also bedestroyed. The oxidizable source can also be an article or object onwhich oxidizable material is affixed or positioned, such as a kitchen orbathroom surface, including utensils, flatware, plates, sinks,countertops, and the tub and shower areas, appliance surfaces, as wellas stains on clothing.

[0082] The concentrated effluent containing a high concentration ofchlorine dioxide can be achieved and maintained by holding the effluentat temperatures below about 5 degrees centigrade, and/or reducing oreliminating sunlight. The effluent can be stored in glass-lined andchemically-resistant plastic surfaced containers.

[0083] When chlorine dioxide oxidizes an oxidizable material, such as amicroorganism or a bleachable stain, the chlorine dioxide releases oneof its electron pair and, in the presence of sodium ions, reverts backto sodium chlorite. Because the method and apparatus of the presentinvention can convert chlorite into chlorine dioxide in simple,non-membrane electrolysis cells, a preferred system for forming chlorinedioxide from an aqueous solution comprises a means for returning thereverted chlorite salts back to the aqueous feed solution, forsubsequent re-conversion to chlorine dioxide.

[0084] The method of making halogen dioxide, according to anotherpreferred embodiment of the present invention, comprises the steps of:

[0085] (1) providing an aqueous supply solution comprising halogendioxide salt;

[0086] (2) passing a portion of the aqueous supply solution a chamber ofan electrolysis cell, preferably a non-membrane electrolysis cellcomprising an anode and a cathode, and along a passage adjacent to theanode; and

[0087] (3) flowing an electrical current between the anode and thecathode, thereby electrolyzing the aqueous feed solution in the passage,whereby a portion of the halogen dioxide salt is converted to halogendioxide, and forming an aqueous effluent comprising halogen dioxide;

[0088] (4) oxidizing an oxidizable material with the converted halogendioxide in the aqueous effluent, whereby the halogen dioxide revertsback to a halogen dioxide salt; and

[0089] (5) returning the used effluent solution comprising the revertedhalogen dioxide salt back to the aqueous supply solution.

[0090] The oxidizable material can be contacted with the aqueouseffluent containing the halogen dioxide in various ways, such as bypouring or spraying the aqueous effluent onto an oxidizable material oran object having an oxidizable material, or by emerging the material orobject into the aqueous effluent. The used effluent solution comprisingthe reverted halogen dioxide salt can be passed through a filter orother type of separator to remove insoluble or particulate matter,before being returned to be used as, or mixed with, the aqueous feedsolution.

[0091] A preferred embodiment of the present invention comprises halogendioxide generating and re-cycling system, comprising:

[0092] a) a source of an aqueous feed solution comprising a halogendioxide salt;

[0093] b) a non-membrane electrolysis cell comprising an anode and acathode, and having a cell chamber with an inlet and an outlet;

[0094] c) a means for passing the aqueous feed solution into the chamberand along a passage adjacent to the anode, and out of the outlet;

[0095] d) an electric current supply to flow a current through theaqueous solution between the anode and the cathode, to convert a portionof the halogen dioxide salt in the passage to halogen dioxide, andthereby form an aqueous effluent comprising halogen dioxide;

[0096] e) a means for delivering the aqueous effluent into contact witha halogen dioxide depletion target, whereby a portion of the halogendioxide in the aqueous effluent oxidizes the depletion target andreverts back to a halogen dioxide salt; and

[0097] f) a means for returning the depleted effluent comprising thereverted halogen dioxide salt back to the source.

[0098] The means for passing the aqueous feed solution (herein after,“feed means”) into the cell can be a pump, or an arrangement wheregravity or pressure forces aqueous feed solution from a storagecontainer into the cell. The means for delivering the aqueous effluentinto contact with the halogen depletion target can be the feed means, orcan be a separate pump or gravity/[pressure arrangement.

[0099] The system can also comprise a re-circulation line through whicha portion of the effluent solution is returned back to the inlet of theelectrolysis cell. As herein before described, re-circulating theeffluent back to the cell increases the total conversion of the halogendioxide salt to the halogen dioxide product.

[0100] The means for returning the depleted effluent can be a collectiontank with a means, such as any of the feed means, for recycling thedepleted effluent back to the source.

[0101] Specific Embodiments

[0102] In one aspect of the present invention, the electrolytic devicesand/or cells disclosed herein are interfaced with an appliance. Suitableappliances for use in conjunction with the present electrolytic devicesand/or cells include, but are not limited to: refrigerators, waterchillers, water fountains, soda fountains, oral irrigators, waterpurifiers, water coolers, washing machines, dishwashing machines, coffeemakers, faucets and combinations thereof. In one aspect of the presentinvention, the devices and/or electrolytic cells disclosed herein areincorporated into and/or interfaced with a refrigerator, in which casethe water inlet line connected to said refrigerator is disconnected andinstead connected to the inlet an electrolysis device and/or celldescribed herein. In this aspect of the present invention, the subjectelectrolytic device may employ an independent source of power (see“Electrical Current Supply” section of present disclosure), oralternatively, may be configured to use the electrical current supply ofthe refrigerator to which it is connected. Those skilled in the art willreadily appreciate that there exist several means by which to connectthe electrolysis devices disclosed herein to the power supply of asubject appliance, and specifically a refrigerator. Upon connecting thewater inlet line to the inlet of the electrolysis device, an outlet lineis connected from the outlet of the subject electrolysis device to thevacant inlet of the subject refrigerator. The subject electrolysisdevice and/or cell may then be operated to electrolyze the watertraveling through the water inlet line and into the subject appliance.The above-described configuration will function to eradicatemicroorganisms present in the water line of the subject refrigerator.The term “water inlet line” is intended to refer to a water line thatextends from a main water source in a home or dwelling and is connectedto an appliance that uses water.

[0103] In one aspect, the concentration of mixed oxidants suitable foruse in the context of a refrigerator is from about 0.01 ppm to about 2ppm, preferably from about 0.1 ppm to about 1.5 ppm, more preferablyfrom about 0.1 ppm to about 1.0 ppm. Without wishing to be bound bytheory, it is believed that the aforementioned levels of mixed oxidantsare below the taste threshold for human consumers, and thus,undetectable upon consumption of water and/or ice produced from thesubject refrigerator.

[0104] In yet another aspect of the present invention, the electrolysisdevices and/or cells disclosed herein are interfaced with an appliance,and particularly a refrigerator, via placement of the electrolysisdevice and/or cell at a point along the water line of the subjectappliance, and particularly a refrigerator, between the inlet of saidappliance and a water dispensing device of said appliance, andparticularly a refrigerator. In yet another aspect of the presentinvention, the electrolysis devices and/or cells described herein areinterfaced with a subject appliance, and particularly a refrigerator,via placement of the subject electrolytic device and/or cell at a pointalong the water line of the subject appliance, and particularly arefrigerator, between the inlet of the subject appliance and anice-making and/or dispensing device of said appliance.

[0105] In one aspect of the present invention, the electrolysis deviceand/or cell interfaced with an appliance is physically located in thesubject appliance. In another aspect of the present invention, theelectrolysis device and/or cell interfaced with the subject appliance isphysically located outside the body of the subject appliance. In yetanother aspect of the present invention, the electrolytic devices and/orcells disclosed herein are interfaced with a refrigerator, in which casesaid electrolytic devices and/or cells are refrigerated. In anotheraspect of the present invention, the electrolytic devices and/or cellsdescribed herein are interfaced with a refrigerator via placement of theelectrolysis device and/or cell in the refrigerator, yet the subjectelectrolytic device is not refrigerated.

[0106] In yet another aspect of the present invention, the electrolysisdevices and/or cells interfaced with an appliance as described hereinfurther comprise a sensor device or similar means for detecting,measuring and/or displaying the level of mixed oxidants generated by thesubject electrolysis device and/or cell. In one aspect, a sensor deviceis placed downstream from the electrolysis device and/or cell. Inanother aspect of the present invention, the sensor device furthercomprises a means for controlling the generation of mixed oxidants bythe subject electrolysis device and/or cell. In yet another aspect ofthe present invention, the sensor device comprises a means forincreasing and/or decreasing the level of mixed oxidants produced by theinterfaced electrolysis device and/or cell. In another aspect of thepresent invention, the sensor device or similar means comprises a meansof controlling the generation of mixed oxidants. Suitable means forcontrolling the generation of mixed oxidants by the subject electrolysisdevice and/or cell, include but are not limited to: standard filters,carbon filters and combinations thereof.

[0107] It should be noted and underscored that the above recitation ofspecific embodiments is in no way intended to limit the scope of thepresent invention. To reiterate, the electrolysis devices and/or cellsof the present invention are suitable for incorporation into, andinterface with, a variety of appliances. The particular configuration ofany such appliance will depend upon several factors, including but notlimited to: the nature of the appliance in which incorporation of thepresent electrolysis devices and/or cells is intended; the specificfeatures and/or power requirements of the subject electrolysis deviceand/or cell for which incorporation is desired; and the needs and/orabilities of the practitioner. Moreover, although the above disclosureis, in part, directed to the interface of the present electrolyticdevices and/or cells with a refrigerator, the devices disclosed hereinare suitable for interface with a variety of household appliances. Aspecific class of household appliances suitable for use in conjunctionwith the electrolysis devices and/or cells disclosed herein are thoseappliances associated with a water inlet and/or outlet. Of course, theelectrolysis devices and/or cells disclosed herein are particularlyeffective for placement before and/or after the water inlet of a subjectappliance, and are highly effective in eradicating microorganisms fromwater entering and/or exiting the subject appliance. Other appliancescomprising a water inlet and/or water outlet, though not specificallyrecited herein, are suitable for use in the context of the presentinvention.

EXAMPLES Example 1 Interface of Electrolytic Device and/or Cell withHousehold Refrigerator

[0108] The refrigerator includes some form of water inlet whereas thewater may be dispensed for drinking via a water dispenser or the watermay be frozen for ice making in the freezer compartment. The presentelectrolysis device and/or cell is placed in line with the inlet watersupply either before or after the water line is connected to therefrigerator. The present electrolysis device and/or cell, in or out ofthe refrigerator, has an inlet port to which the water supply isconnected to and an outlet port to which is connected to therefrigerator before the ice maker and water dispenser (see FIG. 1). Thepresent electrolysis device and/or cell may be placed before the wateris chilled, where the water is chilled or after the water is chilled.The present electrolysis device and/or cell may be activated by theicemaker or the water dispenser via an on-off valve. To avoid reducingthe volume of useable space for food storage in the refrigeratorcompartment, the present electrolysis device and/or cell may not be putinside the chilled area of the refrigerator compartment. The presentelectrolysis device and/or cell may or may not require periodicreplacement depending on the making of the device. The presentelectrolysis device and/or cell may be manually or automaticallyactivated to produce the desired antimicrobial concentration of mixedoxidants. In the case where is in automatically activated, a feedbacksensor is placed at or after the outlet port of the present electrolysisdevice and/or cell and the concentration of the mixed oxidant isadjusted based on the outlet concentration. The adjustment may takeplace via simple on-off activation, as in a home heating system, or viaactive sensing and adjustment of the overall power feeding into thepresent electrolysis device and/or cell. The below diagram illustratesthe above-described configuration.

[0109] All documents cited are, in relevant part, incorporated herein byreference. The citation of any document herein is not be construed as anadmission that the subject reference is prior art with respect to anyaspect of the present invention.

[0110] While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A halogen dioxide generating system, comprising:a) a source of an aqueous feed solution comprising a halogen dioxidesalt; b) a non-membrane electrolysis cell comprising an anode and acathode, and having a cell chamber with an inlet and an outlet; c) ameans for passing the aqueous feed solution into the chamber and along apassage adjacent to the anode, and out of the outlet; and d) an electriccurrent supply to flow a current through the aqueous feed solution inthe passage, to convert a portion of the halogen dioxide salt to halogendioxide, and thereby form an aqueous effluent comprising halogendioxide.
 2. The halogen dioxide generating system of claim 1 wherein theanode and the cathode are confronting and co-extensive, with a chambergap of 0.5 mm or less.
 3. The halogen dioxide generating system of claim1 wherein the anode is a metallic porous anode.
 4. The halogen dioxidegenerating system of claim 1, wherein said system is interfaced with anappliance.
 5. The halogen dioxide generating system of claim 4, whereinsaid appliance is selected from the group consisting of refrigerators,water chillers, water fountains, soda fountains, oral irrigators, waterpurifiers, water coolers, washing machines, dishwashing machines, coffeemakers, faucets and combinations thereof.
 6. The halogen dioxidegenerating system of claim 4, wherein said system is interfaced withsaid appliance via connection of a water inlet line to the inlet of saidelectrolysis cell and connection of an outlet line from the outlet ofsaid electrolysis cell to an inlet of said appliance.
 7. The halogendioxide generating system of claim 4, wherein said system is interfacedwith said appliance via connection of said electrolysis cell between aninlet of said appliance and an outlet of a water-dispensing device ofsaid appliance.
 8. The halogen dioxide generating system of claim 4,wherein said system is interfaced with said appliance via connection ofsaid electrolysis cell between an inlet of said appliance and an outletof an ice-dispensing device of said appliance.
 9. A halogen dioxidegenerating and re-circulating system, comprising: a) a source of anaqueous feed solution comprising a halogen dioxide salt; b) anon-membrane electrolysis cell comprising an anode and a cathode, andhaving a cell chamber with an inlet and an outlet; c) a means forpassing the aqueous feed solution into the chamber, and along a passageadjacent to the anode, and out of the outlet; d) an electric currentsupply to flow a current through the aqueous solution between the anodeand the cathode, to convert at least a portion of the halogen dioxidesalt in the passage to halogen dioxide, and thereby form an aqueouseffluent comprising halogen dioxide; e) a means for delivering theaqueous effluent into contact with a halogen dioxide depletion target,whereby a portion of the halogen dioxide in the aqueous effluentoxidizes the depletion target and reverts back to a halogen dioxidesalt; and f) a means for returning the depleted effluent comprising thereverted halogen dioxide salt back to the source.
 10. The halogendioxide generating system of claim 9, wherein said system is interfacedwith an appliance.
 11. The halogen dioxide generating system of claim10, wherein said appliance is selected from the group consisting ofrefrigerators, water chillers, water fountains, soda fountains, oralirrigators, water purifiers, water coolers, washing machines,dishwashing machines, coffee makers, faucets and combinations thereof.12. The halogen dioxide generating system of claim 10, wherein saidsystem is interfaced with said appliance via connection of a water inletline to the inlet of said electrolysis cell and connection of an outletline from the outlet of said electrolysis cell to an inlet of saidappliance.
 13. The halogen dioxide generating system of claim 10,wherein said system is interfaced with said appliance via connection ofsaid electrolysis cell between an inlet of said appliance and an outletof a water-dispensing device of said appliance.
 14. The halogen dioxidegenerating system of claim 10, wherein said system is interfaced withsaid appliance via connection of said electrolysis cell between an inletof said appliance and an outlet of an ice-dispensing device of saidappliance.